1. Field of the Invention
The present invention relates to small internal combustion engines of the type used with lawnmowers, lawn tractors, and other utility implements. In particular, the present invention relates to an emissions control system for such engines.
2. Description of the Related Art
Small internal combustion engines of the type used with lawnmowers, lawn tractors, and other small utility implements typically include an intake system including a carburetor attached to the engine which mixes liquid fuel with atmospheric air to form a fuel/air mixture which is drawn into the engine for combustion.
One known type of carburetor includes a fuel bowl containing a supply of liquid fuel which is drawn into the throat of the carburetor to mix with atmospheric air during running of the engine. A float within the fuel bowl actuates a valve which meters liquid fuel into the fuel bowl from a fuel tank. In another known type of carburetor, a diaphragm pump attached to the crankcase of the engine is actuated by pressure pulses within the engine to pump fuel from a fuel tank into a fuel chamber within the carburetor, from which the fuel is drawn into the throat of the carburetor to mix with atmospheric air.
In each of the foregoing arrangements, the carburetor is attached via a fuel line to a fuel tank, which stores a quantity of liquid fuel. The fuel tank includes a filler neck through which fuel may be filled into the fuel tank, and a fuel tank cap is attached to the filler neck to close the fuel tank. The fuel tank cap usually includes a venting structure for allowing any pressurized fuel vapors within the fuel tank to vent through the fuel tank cap to the atmosphere. Also, the venting structure allows atmospheric air to enter the fuel tank from the atmosphere as necessary to occupy the expanding volume within the fuel tank which is created as the fuel within the fuel tank is consumed by the engine.
A problem with the existing intake and fuel supply systems of such small internal combustion engines is that fuel vapors may escape from the fuel supply systems to the atmosphere, such as from the carburetor or from the fuel tank. For example, in a float bowl type of carburetor, fuel vapors may escape to the atmosphere via the internal venting structure of the carburetor which connects the air space of the fuel bowl with the carburetor throat, or through the fuel circuit of the carburetor. Also, fuel vapors in the fuel tank may escape to the atmosphere through the venting structure in the fuel tank cap.
What is needed is a fuel supply system for small internal combustion engines which prevents the escape of fuel vapors to the atmosphere, thereby controlling and/or substantially eliminating fuel vapor emissions from such engines.